Using the High Pass Filter to Boost Image Contrast

The High Pass filter is often used to sharpen or even soften image details but did you know that you can also use it to create a high contrast image? If you want your image to have a high contrast effect, there are many ways to achieve this in Photoshop and this filter is one of many effective ways to do it. In this tutorial, we will show how using the High Pass filter can enhance your image and give it more impact. 

It must be said that each image is different and the High Pass filter might show great results with some but not with others. Also, there are many other adjustment settings that you can use in connection with the filter to get various results. For this tutorial, we will be using Photoshop CS2 as the photo editing program although you can use another if it has the High Pass filter option.

Step 1:

Open your image and create a duplicate layer so you can leave your original image untouched. Click on Image > Adjustments > Hue/Saturation and a dialog box will appear. Another way is to make it show is to click on the half black, half white circle under the Layers palette and choosing Hue/Saturation. Drag the saturation slider to around +15 then press OK.

hpcont1stlayer Using the High Pass Filter to Boost Image Contrast

Step 2:

Create a new adjustment layer, this time using brightness/contrast, drag the contrast slider to +15 and press OK.

Step 3:

Press Shift+Ctrl+Alt+e if you are using a PC (if on a Mac it is Shift+Alt+Cmd+E) in order to merge all these document layers into one new layer on top of all the others.

Step 4:

While targeting the new layer, go to Blending mode and choose Soft Light. You can use other blending modes such as Hard Light or Overlay if you want a stronger effect. If it is too strong to the point of being unappealing, you can reduce the opacity to tone it down. For this tutorial, we will be using Soft Light to show a more subtle effect.

hpcont2layer2 Using the High Pass Filter to Boost Image ContrastStep 5:

Click on the Add Layer Mask icon found at the bottom of the Layers palette to add a layer mask to the top layer.

 

Step 6:

Select the Brush tool and set the Hardness to 0%, the Opacity to around 50%, and the Mode to Normal. Make sure the foreground color is black and set the diameter to a manageable size. Now paint over the areas where you want to retain defined detail. Your brushstrokes will reveal the layer beneath it that is still in clear focus. In the meantime, the layer mask will show black lines which represent the strokes you are making. 

Step 7:

Again, merge all the document layers into one new layer and set the Blending Mode to Soft Light. Next, go to Filter > Other > High Pass and set the radius value to around 3 pixels, depending on the image size and content. You can check the image preview and work at a suitable value based on the results shown. 

hpcont2hp Using the High Pass Filter to Boost Image Contrast

Here is a comparison between the original image and the final result after using the High Pass Filter:

hpcontcomp Using the High Pass Filter to Boost Image Contrast


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Using the High Pass Filter to Create a Soft Effect

The high pass filter is often used for sharpening images but it can also be used to have an opposite effect, which is to soften the details of an image. The softening can be applied to the whole image or just selected areas, leaving key details sharp and focused. 

A soft, diffused look is often used when you want to soften the texture of skin or if you want to create a dreamy effect. In this tutorial, we will explain how the high pass filter can be used for this purpose. Photoshop CS2 is the photo editing program used but other programs that include the high pass filter will also be sufficient in getting great results.

hporig Using the High Pass Filter to Create a Soft EffectStep 1:

Open your image and create a duplicate layer. If you have an existing image opened that has adjustments, create a new layer with a flattened version of the image. Click on the top layer to target it and then click Layer > New > Layer. Choose the new layer you created and press Ctrl + Alt + Shift + E (if on a Mac it is Command + Option + Shift + E).

Step 2:

Go to Filter > Other > High Pass and a dialog box will pop up showing an image preview and the radius settings below it. Note that the higher the radius value, the softer the image will turn out. For this tutorial we will be setting the radius value at 15.

hphighpass Using the High Pass Filter to Create a Soft Effect

Step 3:

Now time for some diffused lighting! Go to Image > Adjustments > Invert so that only the areas that were untouched by the filter will be affected. Go to the Blending Mode dropdown list at the Layers Palette and choose Soft Light to produce a soft focus look. If you are happy with the overall appearance of the image, this can be your final adjustment. But if there are areas you prefer to remain sharp then proceed to the next step.

hpsoftlight Using the High Pass Filter to Create a Soft Effect

Step 4:

For this next step, we will be creating a layer mask where we can show the parts of the underlying layer which are still defined and clear. By clicking on the Add Layer Mask icon found at the bottom of the Layers palette, a layer mask is added. This appears as an empty white rectangle beside the active layer.

Step 5:

Now go to the Brush tool and set the Hardness to 0% so that the edges are at their softest. Keep the mode at Normal, the foreground color should be black and have the Opacity at around 80%. The brush diameter should be just large enough to trace the details you want to keep sharp without affecting the irrelevant areas. With the brush, paint over the areas that you want to remain sharp. You will notice that the sections you are painting are revealing the matching areas of the layer beneath it which are sharp. These parts that you are brushing will appear black in the layer mask.

hplayer Using the High Pass Filter to Create a Soft Effect

Note that if you think you overdid the brushing and want the revealed areas to be more hidden, just set the foreground color to white and paint over the selected areas. This will bring back the details from the top layer. To lessen the strength  of the overall blurriness, you can adjust the opacity or fill to a lower degree. 

Using the High Pass Filter to soften images is just one of many ways to achieve similar results in Photoshop. Also, some images could benefit more with other soft focus techniques compared to the High Pass option so if you don’t like how your image turns out with this method, try experimenting with other options.

hpcomp Using the High Pass Filter to Create a Soft Effect


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How to Use the High Pass Filter to Sharpen Images

Photo editing programs offer various methods for you to sharpen your photos and the High Pass filter is one of the easiest yet most effective tools for the job. It selects the edges found in the image and sharpens them without affecting the areas that have no edges.

People have personal preferences over which sharpening tool works best for them and the High Pass filter is arguably the most popular for good reasons. One is that it locates the edges for you and you don’t have to manually select areas as you would with the Sharpen filter or Unsharp Mask (insert link to unsharp mask article). Another reason is that adjusting the filter is very simple since there are less settings to tweak compared to the others; in fact there is only one (unlike the Unsharp Mask which has three settings and the Smart Sharpen which has even more.) 

Here is a short tutorial on how to use the High Pass filter. Adobe Photoshop CS2 is used for this purpose and you might be using another photo editing program, but the concept works the same. If it is your first time ever to use this technique, you would be surprised by how quickly you will get the hang of it and make it a part of your post processing routine. 

Step 1: 

Open a copy of your original image (one can’t be too careful with keeping the original image safe!) and create a duplicate layer. The keyboard shortcut is Ctrl + J for Windows and Command + J for Mac. 

Step 2:

Change the duplicate layer’s blend mode from ‘Normal’ to ‘Overlay.’ You can find the blend mode options in the Layers Styles dialog box at the bottom right of the screen. The High Pass Filter works by turning to neutral gray all the areas of the image that do not have edges and the Overlay blend mode keeps all neutral gray areas from being adjusted. Therefore, the neutral gray areas will not be included in the sharpening. 

When you click on the Overlay blend mode, your image will suddenly appear to have more contrast like this:

highpassoverlay How to Use the High Pass Filter to Sharpen ImagesThis saturated effect will disappear once we click on the High Pass filter. 

Step 3:

While still highlighting the duplicate layer, click on the Filter menu (found on the toolbar on top of the screen) and choose ‘Other’ from the dropdown list, and then click on ‘High Pass.’ The High Pass dialog box will appear showing the preview of an area of the image in gray (edges are darker gray), the preview option and the one and only setting we mentioned earlier, the Radius setting. 

The Radius slider controls the amount of sharpening to be applied around the edges. Dragging the slider to the right will increase the radius value (in pixels) and affect a bigger area, while sliding it to the left reduces the intensity of the effect. By keeping the preview checkbox ticked, you can see how the image in the main screen is affected when you move the radius left or right. 

How much radius value to use depends on the pixel dimension of your image. Generally, the larger the image size, the higher the radius value you’ll need to use. A sign that you’re going overboard with the radius value is when halo effects begin to show up around the edges of details. This image size is rather small so a radius value of 1 pixel is enough to sharpen the edges without causing ill effects from oversharpening. 

highpass How to Use the High Pass Filter to Sharpen Images

Once you have chosen the radius value, just press ‘OK’ and you’re all done!

The photos below show the difference between the unedited image (photo on left) and the result of using a High Pass filter (photo on right):

hpf How to Use the High Pass Filter to Sharpen Images

Notice that the areas with edges, especially the hair, eyes, lips and the yellow curls, have become more defined while the areas with no edges, namely the cheeks, have remained smooth. 


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